JPH0641938B2 - Nondestructive measurement method for zirconium alloy materials - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a nondestructive measurement method for zirconium alloy materials, and more particularly to hydrogen in zirconium alloy materials affected by hydrogen, such as pressure tubes in heavy water reactors. The present invention relates to a measuring method suitable for measuring and evaluating the concentration and the strength of an alloy material.

[Conventional technology]

As an example of the conventional embrittlement measurement method, Yashima and 2 others "Detection of hydrogen erosion by ultrasonic flaw detection""Non-destructiveinspection" Vo
l. 34, No. 2A, ppl18-119, February 1985. Here, in carbon steel and low-alloy steel, the location where the acoustic impedance changes due to decarburization due to hydrogen attack or grain boundary cracking can be measured by ultrasonic echo.

[Problems to be solved by the invention]

In a zirconium alloy, hydrogen does not erode into the crystal to cause embrittlement, but hydrogen that has not completely dissolved in the zirconium alloy chemically reacts with the zirconium alloy to form a hydride (ZrH ₂ ). , Which precipitates in the zirconium alloy and causes embrittlement.

In this way, in the case of embrittlement of a material due to precipitation, the properties of hydride are almost the same as those of the original metal, and the acoustic impedance of the material hardly changes. Can not detect the degree of. Further, when the measurement is performed in an actual plant, it is difficult to accurately measure the attenuation of the ultrasonic wave because the reflectance and the transmittance of the ultrasonic wave change depending on the surface state of the sample. From these things, in the above-mentioned prior art, it was not possible to detect the hydrogen concentration and the degree of hydrogen embrittlement without considering the change of the zirconium alloy due to the precipitation of hydride.

On the other hand, as an example of an eddy current test method (hereinafter referred to as ECT), there is JP-A-55-141653 "deterioration state determination method for strong precipitation hardening type iron-based alloy".
In this conventional example, the deterioration state of the iron-based alloy is measured by the EC of the measured material.
The T value is compared with the ECT value of the material to be measured before use or a material of the same kind as that of the material subjected to the same heat treatment as the initial heat treatment of the material to be measured, and it is determined whether the value is positive or negative. Shows how.

However, since it is only judged by the positive and negative,
No quantitative measurement was possible, and no consideration was given to the above-mentioned hydride precipitation problem peculiar to zirconium alloys.

[Object of the Invention]

An object of the present invention is to non-destructively measure a hydrogen concentration and strength of an alloy (degree of embrittlement) with high accuracy and in a short time for hydrogen embrittlement of a precipitation type such as a zirconium alloy material. It is to provide a measuring method.

[Means for solving problems]

The present invention focuses on the fact that the electrical characteristics of a zirconium alloy change depending on the amount of hydride generated inside, and detects the unbalanced voltage between the reference material and the measured object using an AC bridge, and The present invention provides a nondestructive measurement method for a zirconium alloy material, which determines the hydrogen concentration in the zirconium alloy consisting of size and phase angle and the degree of embrittlement of the alloy.

Specifically, two measurement methods are proposed.

First, in the first method, one reference material is selected, data is taken while changing the frequency of the AC bridge between it and the object to be measured, and when the maximum unbalance voltage is below a certain threshold value, When the measured material has the same characteristics as the reference material and the maximum unbalance voltage exceeds the threshold value, the hydrogen concentration in the zirconium alloy and the strength of the zirconium alloy (hydrogen embrittlement) And the degree).

On the other hand, in the second method, while changing the reference material,
Data is taken while changing the frequency of the AC bridge between them and the object to be measured, and the hydrogen concentration or strength of the reference material that minimizes the absolute value of the maximum unbalanced voltage is determined as the characteristic of the object to be measured.

In any of the methods, it is possible to adopt means for canceling the offset due to the influence of oxides generated on the surface and means for accurately detecting the amount of hydride in the radial direction and the amount of hydride in the circumferential direction of the zirconium alloy pipe. Yes,
The judgment result is quantitative.

[Action]

As shown in FIG. 3, the hydride 13 such as the zirconium alloy 12 is deposited in a substantially planar form, so that the toughness of the zirconium alloy decreases in proportion to the amount of the hydride.

The resistivity ρ _Zr of zirconium alloy is about 0.49 × at 30 ℃.
It is 10 ⁻⁶ (Ωm), and its hydride is known to have an intermediate value ρ _{ZrH 2} between metal and semiconductor. The present invention _utilizes this relationship of ρ _Z << ρ _ZrH2 to detect the amount of hydride and the degree of embrittlement accompanying it from the amount of change in resistivity in the zirconium alloy.

When a coil is arranged on a zirconium alloy as shown in FIG. 4 and an alternating current is applied, an eddy current is induced in the alloy. Therefore, if a probe coil is connected to the two impedances of the AC bridge shown in FIG. 5, the reference material is placed in one coil, and the measured object is pressed against the other coil, the impedance due to the difference in eddy current The amount of hydride can be detected from the disequilibrium of.

The AC bridge is highly accurate because it detects only the amount of change in impedance between the two. Also, since a lot of information can be obtained while changing the frequency, the reliability of the measurement result is sufficient.

〔Example〕

 Next, an embodiment of the present invention will be described with reference to the drawings.

FIG. 1 is a diagram showing an example of a system configuration for carrying out the nondestructive measurement method for a zirconium alloy material according to the present invention. In the figure, reference numeral 1 is a pressure tube of a zirconium alloy material used in a nuclear power plant or the like, which is an object to be measured.
Further, 2A, 2B, 2C and 2D are probe coils, 3 is a scanning drive device thereof, 4 is a scanning drive control device, 5 is an eddy current flaw detector, 6 is a computer, 7 is an external storage device, and 8 is an external recording device. It is a device. Probe coils 2A and 2B are arranged on the surface of the DUT 1, and probe coils 2C and 2D are arranged on the surface of the reference test piece 11.

The details of the scanning drive device 3 are shown in FIG. The probe coils 2A, 2B, 2C, 2D are pressed against the DUT 1 and the reference test piece 11 by the motor 11 via the ball screw mechanism 29. The pressing force is detected by the load cell 21. Each probe coil can be moved on the rail 23 by the positioning motor 26 and can be accurately positioned in a wide range. The device under test 1 and the plurality of reference test pieces 11 are mounted on the table 2
Set on 5. Rails 23 are pillars 24 and stand 2
It is fixed on 5. The long object 1 is a roller 2
8 and is driven by a motor 27 in the axial direction to change the position.

The motor of the scan drive device 3, other drive units, and the signal system are
It is connected to the scan drive controller 4 and receives control.

The four probe coils have a coil shape of 1 mm in diameter and 7 turns.
The one with 0 turns is embedded in the insulating resin and has the same characteristics. These probe coils are connected to an eddy current flaw detector 5 having an AC bridge circuit, and equivalently form the circuit shown in FIG.

The eddy current flaw detector 5 has a frequency range of 5 KHz to 5 MHz,
It has an automatic balancing function. The absolute value and the phase angle of the unbalanced voltage measured here are converted into a digital signal and taken into the computer 6.

The computer 6 controls the drive control device 4, the eddy current flaw detector 5, the external storage device 7, and the external recording device 8 via the interface. In this case, a 16-bit CPU is used as the computer 6, and a floppy disk is connected as a parallel storage device as an external storage device 7. Further, data is exchanged with the drive control device 4 via a peripheral interface adapter (PIA), and with the eddy current flaw detector 5 via a GP-IB interface.

Now, the main routine for executing the measuring method of the present invention in the system configured as described above will be described with reference to the flow chart of FIG.

First, the drive unit 3 is arranged on the surface of the DUT 1 such as the pressure tube of the nuclear reactor, and the drive unit 3 is set at the origin of the measurement system.
Therefore, the inspection range for hydrogen embrittlement and the measuring method described later are selected and input from the computer 6. When the measurement is started, the drive device 3 moves to the measurement start point and measures the eddy current according to the input measurement method. After the measurement is completed, the driving device 3 moves to the next measurement position. The inspection is repeated in the same manner, and is continued until the drive device 3 reaches the final position. The data being measured is stored in the floppy disk 7. After measurement,
Measured data is from floppy disk 7 to computer 6
Is taken back into. This data is processed by a data processing method corresponding to the previously specified measurement method, and serves as a material for determining the hydrogen concentration and the strength of the alloy (degree of hydrogen embrittlement). The result is output to the external recording device 8 or displayed on the CRT of the computer.

As mentioned above, there are two measurement methods.

FIG. 7 is a flow chart showing the data collection stage of the first measurement method, and shows the inside of block A in FIG. 6 in detail. Here, first, the frequency is determined (≧ 5K
Hz). Next, when the H ₂ concentration is 25 ppm or less, the hydride Zr
The probe coil 2 is attached to the reference test piece 11 on which H ₂ is not deposited.
C and 2D are pressed to achieve equilibrium, then the probe coil 2D is lifted off (lifted), the lift-off signal is set to a phase angle of 0 °, and the offset value to be cancelled is measured. After pressing the probe coil 2A against the inner surface of the pipe (measurement target) 1, the probe coils 2A and 2D
Then, the absolute value of the unbalanced voltage between the probe coils 2A and 2C and the phase angle are measured by the eddy current flaw detector 5. This data is stored in the floppy disk 7 via the computer 6. After that, the frequency is increased by Δ and the routine is repeated again. When the frequency reaches ≧ 5 MHz, the measurement is ended and the data processing is started.

The frequency range of this embodiment was determined in consideration of the thickness of the zirconium pressure tube being 4 mm and the skin effect. The skin effect is given by the following equation.

Here, δ is the penetration depth, that is, the depth that becomes 1 / e of the surface current, ω is the angular velocity (2π), μ is the magnetic permeability, and ρ is the resistivity. For zirconium alloys, μ = μoμ _Zr , μ
_Zr ≈1.0, ρ = 0.49 × 10 ⁻⁶ (Ωm at 2
Therefore, the relationship between the frequency and the penetration depth δ of the eddy current is as shown in FIG. Since the thickness of the pressure tube 1 is 4 mm, the frequency band is set to the range of 5 KHz to 5 MHz, and the resonance frequency _{o of the} probe coil is set to the intermediate 300 KHz.
And

Although it has been stated that the measurement data is temporarily stored in the floppy disk, if the internal memory such as DRAM in the computer 6 has sufficient capacity, it may be stored there and the speed of the data processing in the next stage Of course, it will be much better. Also, a larger capacity hard disk can be used.

The data processing corresponding to the above data collection of the first measurement method is shown in a flow chart in FIG. Floppy disc 7
The data of the measurement position, the absolute value of the unbalanced voltage, and the phase angle, which are stored in, are loaded into the computer 6. The absolute value | V | of the maximum unbalanced voltage is smaller than the reference threshold value V _th (| V
When | <V _th ), it is determined that the portion of the object to be measured has the same hydrogen concentration as the reference test piece or strength as an alloy. On the contrary, if it is large, the
As shown in the center of the figure, the hydrogen concentration and the fracture toughness value are calculated using the calibration curve obtained in advance. Next, the value evaluated as the measurement position is output to the external recording device 8, and the same routine is repeated for other measurement positions.

The outline of this first measurement method is summarized in FIG. 9 and FIG.
It looks like Figure 0. As shown in FIG. 9, the probe coil 2A is used as the DUT 1, and the probe coil 2C is used as the reference test piece 1.
The unbalanced voltage when placed at 1 draws a pattern as shown in FIG. At this time, the maximum unbalanced voltage appears at the resonance frequency _o . When the absolute value | V | is smaller than the threshold value, it is determined that it is the same as or close to the reference test piece, and when it is larger, the hydrogen concentration in the alloy and the strength of the alloy are calculated from the information of the phase angle θ.

Although the probe coil 2A is located outside the pressure tube 1 in FIG. 1, it is located inside the pressure tube 1 in FIG. 9, but hydrogen is considerably free in the metal under the temperature condition of about 280 ° C. of the atomic plant. Since the pressure pipe used for a long time can be moved, it is considered that there is not much difference between the measured values inside and outside.

The second measuring method will be described with reference to FIGS. 11 to 14. FIG. 11 is a flowchart showing the data collection of the second measuring method, and FIG. 12 is a flowchart showing the data processing.

In the data collection of the second measurement method, first, the frequency is determined (≧ 5 KHz). The probe coils 2A and 2B are pressed against the inner surface of the pipe 1 for equilibrium, the probe coil 2B is lifted off, and the lift-off signal is set to a phase angle of 0 °. Next, the probe coil 2C is pressed against the inner surface of the pipe 1 to switch between the probe coils 2B and 2C, and the eddy current flaw detector 5 determines the absolute value and the phase angle of the unbalanced voltage of the probe coils 2A and 2C. taking measurement. This data is transferred from the computer 6 to the floppy disk 7 and stored. Then, the reference test piece 11 is exchanged with another one, and a similar routine is performed. After measuring a plurality of reference test pieces having different hydrogen concentrations, the frequency is increased by Δ and the above routine is repeated again. When the frequency reaches ≧ 5 KHz, the data collection is completed and the data processing is started.

In the data processing of this measurement method shown in FIG. 12,
The measurement position, the absolute value of the unbalanced voltage, and the phase angle data stored in the floppy disk 7 are loaded into the computer 6, and the absolute value of the maximum unbalanced voltage in each reference test piece | V
| Is compared, and the hydrogen concentration of the reference test piece showing the smallest value or the strength as an alloy is determined as the measured value of the measured object. At this time, when the number of reference test pieces is large (that is, when a large number of specimens having slightly different characteristics are prepared in order to improve accuracy), it may not be possible to immediately judge from the characteristic pattern by visual observation. In order to avoid this, the true minimum value may be found by optimizing the relationship between the hydrogen concentration of the reference test piece and the absolute value of each unbalanced voltage, or by using the least square method or the like. The measurement position and the evaluation result are output to the external recording device 8, the measurement position is moved to the next measurement position, and the same routine is repeated.

A summary of the second measuring method is shown in FIGS. 13 and 14.
It becomes like the figure. As shown in FIG. 13, the unbalanced voltage when the probe coil 2A is placed on the DUT 7 and the probe coil 2C is placed on the plurality of reference test pieces 11 in sequence is as shown in the pattern of FIG. Become. Here, since the unbalanced voltage with the m-th reference test piece is the minimum, it is determined that the hydrogen concentration of the DUT 1 is equal to that of the m-th reference test piece.

FIG. 15 shows an example of the result measured by the first measuring method. A standard test piece having a hydrogen concentration of 25 ppm or less and no hydride was used. Looking at the patterns of the unbalanced voltage traces for the three types of measured objects a, b, and c having different hydrogen concentrations, the unbalanced voltage of a, which is almost the same as the reference test piece, is small. Pipe b having a hydrogen concentration of about 100 ppm has an absolute value of unbalance voltage of 1 volt at the maximum and a phase angle of about 210 °, and pipe C having a hydrogen concentration of about 400 ppm has the same value of 2 volt and about 350 °. . Thus, the absolute value of the unbalanced voltage and the phase angle change depending on the hydrogen concentration. At this time, the maximum unbalanced voltage appears at = 300 KHz.

FIG. 16 is a diagram showing the effect of lift-off caused by the generation of ZrO _{2 on the} surface of the object to be measured and the method of the cancellation. The solid line shows the result of measurement with the same pipe material with the ZrO ₂ oxide film present, and the dotted line shows the result of measurement after removing the ZrO ₂ oxide film. Frequency = 5KHz
The lift-off component at time is represented as the difference between the maximum unbalanced voltages. Therefore, it is understood that the influence of the oxide film can be canceled by the lift-off voltage at = 5 KHz or a low frequency. In both measurement methods, the lift-off signal is obtained in the early stage of data acquisition in order to determine the value that is the basis of this cancel.

In the above embodiment, the coil shown in FIG. 19 is used, but since the eddy current flows parallel to the surface, it is suitable for detecting hydride in the radial direction, which greatly affects the strength of the object to be measured. . However, since hydrides easily move due to stress, temperature, etc., they are not always aligned only in the radial direction (see FIG. 3). Therefore, as shown in FIG. 18, a probe is used in which a coil 213 is placed in parallel to flow an eddy current perpendicularly to the surface and a powdered sintered iron core 212 is formed into a horseshoe shape and inserted. According to this probe coil, the amount of hydride in the circumferential direction can be accurately detected. When the probe coils shown in FIGS. 18 and 19 are used together,
It is possible to accurately measure the hydrogen concentration and the degree of hydrogen embrittlement.
In these figures, 211 is an insulating resin.

〔The invention's effect〕

According to the present invention, with respect to precipitation-type hydrogen embrittlement such as a zirconium alloy material, the hydrogen concentration and the strength (degree of embrittlement) of the alloy can be measured with high accuracy and in a short time. A measurement method will be obtained.

[Brief description of drawings]

FIG. 1 is a diagram showing an example of a system configuration for carrying out the method for measuring the destruction of a zirconium alloy material according to the present invention, FIG. 2 is a diagram showing the details of a scanning drive device, and FIG. 3 is a diagram showing hydrogen in a zirconium alloy. Fig. 4 is a diagram showing the deposition state of oxides, Fig. 4 is a diagram showing eddy currents induced by a coil, Fig. 5 is a diagram showing an AC bridge equivalent circuit of an eddy current flaw detector and a probe coil, and Fig. 6 is this A flow chart showing a main routine for executing the measuring method of the invention, FIG. 7 is a flow chart showing a data collecting step of the first measuring method, FIG. 8 is a flow chart showing a data processing step thereof, FIGS. 9 and 10. The figure is a diagram showing the outline of the first measuring method, and FIG. 11 is the flow chart showing the data collecting step of the second measuring method.
The figure shows the data processing stage of the flow chart, No. 13
Figure and Figure 14 are diagrams showing the outline of the second measurement method,
FIG. 15 is a diagram showing an example of the result of actual measurement by the first measurement method, and FIG. 16 is a diagram showing the effect of lift-off due to the occurrence of ZrO _{2 on the} surface of the object to be measured and its cancel method, FIG. Is a characteristic diagram of the skin effect of zirconium, No. 1
8 and 19 are views showing the shape of the probe coil. 1 ... Zirconium alloy pressure tube, 2A, 2B, 2C, 2D
... probe coil, 3 ... scanning drive device, 4 ... drive control device, 5 ... eddy current flaw detector, 6 ... computer, 7 ... external storage device, 8 ... external recording device, 11 ... reference test piece, 12 ...
Zirconium, 13 ... Hydride (ZrH ₂ ), 21 ... Load cell, 22 ... Transducer pressing motor, 23 ... Rail, 24 ... Pillar, 25 ... Stand, 26 ... Moving motor, 27 ...
Motor for moving object to be measured, 28 ... Rotor, 29 ... Ball screw, 211 ... Insulating resin, 212 ... Powder sintered iron core, 21
3 ... coil.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Tsugio Oyamada 3-1-1, Saiwaicho, Hitachi-shi, Ibaraki Hitachi Ltd. Hitachi factory (72) Inventor Kenichi Suzuki 3-chome, Hitachi-shi, Ibaraki No. 1-1 Hitachi Ltd., Hitachi Plant (72) Inventor Yoji Yoshida 3-2-1, Saiwaicho, Hitachi City, Ibaraki Hitachi Engineering Co., Ltd. (56) Reference JP-A-58-137755 ( JP, A)

Claims (9)

[Claims] 1. A non-destructive measuring method for a zirconium alloy material by an eddy current flaw detection method in which an AC signal is applied to a non-measuring body and a reference test piece and an eddy current generated in them is detected by an AC bridge circuit. A step of selecting one reference test piece and collecting data of the unbalanced voltage and the phase angle of the AC bridge circuit while changing the frequency of the AC signal, and B. Compare the absolute value of the maximum unbalanced voltage with a certain threshold,
When it is smaller than the threshold value, the hydrogen concentration of the reference test piece and the strength as an alloy corresponding to the hydrogen concentration are judged to be the characteristics of the measured object; When it is larger than the threshold value, the maximum unbalance voltage and the phase angle are compared with a calibration curve obtained in advance, and a step for calculating the hydrogen concentration of the measured object and the strength of the alloy is included. Nondestructive measurement method for zirconium alloy materials. 2. The eddy current probe coil according to claim 1, wherein the coils are placed parallel to each other in order to pass an eddy current perpendicularly to the surface of the object to be measured, and the powder sintered iron core is formed into a horseshoe shape. A nondestructive measuring method for a zirconium alloy material, which is a probe coil that is formed and inserted. 3. The radial characteristic of the object to be measured according to claim 2, further comprising the step of collecting data by using a probe coil for flowing an eddy current parallel to the surface of the object to be measured. A nondestructive measuring method for a zirconium alloy material, which comprises separately measuring the component and the characteristic component in the circumferential direction. 4. A method according to claim 1, wherein a lift-off signal at a low frequency at the lower end of the frequency range is subtracted from the unbalanced voltage data, and oxides generated on the surface of the object to be measured. A non-destructive measurement method for zirconium alloy material, which is characterized by canceling the influence. 5. A non-destructive measuring method for a zirconium alloy material by an eddy current flaw detection method in which an AC signal is applied to an object to be measured and a reference test piece and an eddy current generated in them is detected by an AC bridge circuit. B. The step of collecting data of the unbalanced voltage and the phase angle of the AC bridge circuit while changing both the reference test piece and the frequency of the AC signal for one DUT, and B. A nondestructive measuring method for a zirconium alloy material, which comprises: a step of determining the hydrogen concentration of the test piece having the smallest absolute value of the maximum unbalance voltage and the strength as an alloy from the characteristics of the object to be measured. 6. The eddy current probe coil according to claim 5, wherein the coils are placed parallel to each other so that the eddy current flows vertically to the surface of the object to be measured, and the powder sintered iron core is formed into a horseshoe shape. A non-destructive measuring method for a zirconium alloy, which is a probe coil formed and inserted. 7. The characteristic of the object to be measured in the radial direction according to claim 6, further comprising the step of collecting data using a probe coil for flowing an eddy current parallel to the surface of the object to be measured. A nondestructive measuring method for a zirconium alloy material, which comprises separately measuring the component and the characteristic component in the circumferential direction. 8. The lift-off signal at a low frequency at the lower end of the frequency range is subtracted from the unbalanced voltage data according to any one of claims 5 to 7, and the oxide generated on the surface of the measured object is measured. A non-destructive measurement method for zirconium alloy material, which is characterized by canceling the influence. 9. In any one of claims 5 to 8, a minimum of 2 is required for calculating the absolute value of the maximum unbalanced voltage.
A non-destructive measuring method for zirconium alloy material, characterized by using a multiplication method.